How do I bake to specific tiles in a UDIM
Currently blender has no option to bake UDIMs. A workaround for this is to place the uv map you want to bake to the front of the UV tiles. For this create for every tile an image and save it. That is important so blender has the naming schema and you can replace these images with the final bake.

Bake the first image:


Save the bake for later because it will be overwritten.

Now you have to move the UV maps from the second to the first.


Bake again and save the image. Now overwrite the placeholder from step 1 with the same name.

Open the first baked image and in the UV editor press the reload button.